1. Field of the Invention
This invention is directed to the production of storage-stable fertilizer concentrate compositions containing magnesium nitrate and certain plant food nitrogen in aqueous solution, present in particular proportions, as well as to aqueous foliar spray for application on various crops. More particularly, the present invention is concerned with compositions exhibiting improved low salt-out temperatures comprised of eutectic compositions of critical proportions of magnesium nitrate, ammonium nitrate and urea in aqueous solution.
2. Description of the Prior Art
The use of magnesium in various forms as soil fertilizer has been known for many years. Magnesium occurs native as the mineral magnesite (Mg CO.sub.3), widely as dolomite (MgCO.sub.3.CaCO.sub.3), also as the sulfate (MgSO.sub.4) and as the sulfate of potash-magnesia (Mg SO.sub.4.K.sub.2 SO.sub.4). Several forms of magnesia (MgO) are used in the manufacture of fertilizers, especially for potatoes, fruit trees, and tobacco. This product made by calcining magnesite is called calcined magnesite and the product prepared from seawater is called seawater magnesia.
Mixed fertilizers containing plant nutrients such as nitrogen, potassium, phosphorus, calcium and sulfur, in addition to magnesium, are also known in the art. U.S. Pat. No. 1,916,617 issued July 4, 1933 discloses the obtainment of mixed fertilizers containing potash and nitrogen from the nitrates of calcium or magnesium or mixtures of both.
Liquid magnesium-containing fertilizers are also known and have more recently been described in Agrochemia, 1976, 16 (12) pages 344-48 and in Czech Pat. Nos. 145,487 and 165,530, issued Oct. 15, 1976.
The application of nitrogen in the form of urea, or other source of nitrogen, to foliage has also been described in U.S. Pat. No. 2,802,307 issued Aug. 13, 1957, as well as in U.S. Pat. No. 2,663,629, issued Dec. 22, 1953. The application of mixed fertilizers to forested areas including nitrogeneous fertilizers, such as mixtures of urea and ammonium nitrate, together with nominal amounts of mineral supplements, such as salts of magnesium, have more recently been described in U.S. Pat. Nos. 4,033,747 and 4,033,746, issued July 5, 1977. U.S. Pat. No. 4,035,173, issued July 12, 1977, also is concerned with a method for simultaneously fertilizing living commercial timber forests using a combination of nitrogeneous fertilizer solutions of particular dosage.
U.S. application Ser. No. 704,269, of Clapp, Parham Jr., and Johnson filed July 12, 1976, now abandoned, and assigned to the same assignee as in the present application, discloses the use of an aqueous solution of magnesium nitrate, ammonium nitrate and urea on crops as a foliar fertilizer, even when the crops are grown in soils that are very high in soil magnesium. U.S. Pat. No. 3,930,832, issued Jan. 6, 1976, also assigned to the same assignee as in the present application, discloses the inhibition of corrosion of carbon steel by aqueous solutions of zinc nitrate, ammonium nitrate and urea by incorporating therein of an effective amount of a thiosulfate compound. As is apparent from U.S. application, Ser. No. 704,269, the urea and ammonium nitrate ingredients of the magnesium nitrate-containing compositions disclosed therein are incorporated in the composition in the form of a commercial fertilizer solution and hence, these compositions contain on a weight basis, at least about 14%, by weight, of urea, and generally, at least about 20%, by weight, of urea. Furthermore, the commercial magnesium nitrate-ammonium nitrate-urea solution of the aforementioned Application, presently sold as a 16-0-0-4 Mg solution, is characterized by having an ammonium nitrate to urea ratio of about 1.3 to 1, and hence, precipitates solid material, i.e. "salts-out," during storage, transportation or field application at temperatures of about 60.degree. F. It has been found, further, that the lowest possible salt-out temperature for a nitrogen-magnesium formulation containing 16% nitrogen from the commercial fertilizer solution of ammonium nitrate and urea, referred to in said application and 4% magnesium from magnesium nitrate is about 35.degree. F., a temperature which is too high for safe storage and transport in most geographical locations, unless expensive temperature controlled equipment is employed, if available; furthermore, the precipitated solids cannot be conveniently pumped or otherwise handled by apparatus normally used for such solutions. Accordingly, need exists for magnesium nitrate-ammonium nitrate-urea aqueous fertilizer solutions having low salt-out temperatures which are capable of being transported, stored and handled as a liquid concentrate, as well as a sprayable solution.